1. Field of the Invention
The present invention relates to a backrest adjusting device for a chair allowing convenient, stable, and smooth adjustment of the height of the backrest of the chair.
2. Description of the Related Art
FIG. 11 of the drawings illustrates a chair with a conventional height adjusting device, wherein an L-shaped plate 3′ is mounted between a backrest 1′ and a seat 2′. Mounted to a rear of the backrest 1′ is a coupling portion 11′ that engages with an upper end of the L-shaped plate 3′. A tightening knob 12′ is mounted to the coupling portion 11′ and can be turned loose to allow adjustment of the height of the backrest 1′. After adjustment, the tightening knob 12′ is turned in a reverse direction to tighten the L-shaped plate 3′ and, thus, fix the height of the backrest 1′. However, adjustment of the height of the backrest 1′ requires laborsome turning of the tightening knob 12′. Furthermore, the tightening effect is not reliable such that the backrest 1′ is apt to slide.